1. Technical Field
The present invention relates to a method of manufacturing an active matrix type liquid crystal panel that is driven by thin film transistors formed on a glass substrate. Specifically, the present invention relates to a method of manufacturing a liquid crystal panel that is suitable to be applied to a process of printing a sealant on a glass substrate by using a seal plate.
2. Description of the Related Art
Recently, Flat Panel Displays (FPDs), such as liquid crystal displays, have used in many fields including television receivers, computers, and the like due to their light-weight, ultra-thin, and small power-consumption characteristics. According to the diversity of purpose in the market, it is increasing that a demand for not only a yield improvement to improve the productivity but also an improvement of image quality.
A liquid crystal panel includes a pair of glass substrates that face each other with a predetermined gap, which is formed by spacers interposed between the glass substrates, and liquid crystals filled and hold between the glass substrates. One substrate is an active matrix substrate (hereinafter referred to as a “TFT substrate”) where thin film transistors are formed, and the other substrate is a color filter (hereinafter referred to as a “CF”) substrate that face to the TFT substrate. Conduction layers are formed on the respective substrate, and the driving of the liquid crystals is controlled by electrical charge between the conduction layers. A controlling of the driving of the liquid crystals provided on a transistor formed section or a wiring section in a display area of the TFT substrate is harder than controlling the driving of the liquid crystals provided on a pixel region. Thus, a desired display can be provided by intercepting penetration of light by forming of a light shielding layer (black matrix: hereinafter referred to as “BM”) on the CF substrate side that face to the TFT substrate.
As described above, in order to seal the liquid crystals between the two glass substrates, a sealant is applied on the circumference of a display area on the glass substrate, and the pair of glass substrates is combined to each other. There are two principal methods of applying the sealant on the glass substrate as a circumferential seal of the display area, as follows.
A first method is a method that fills a sealant in an injector shaped syringe and applies the sealant on the substrate without lifting the syringe. A second method is a method that prepares a seal printing plate (hereinafter referred to as a “seal plate”) and prints a sealant on the glass substrate. According to the first method, since a seal pattern is applied on the circumference of the display area without lifting, the sealant does not contact with the display area of the panel, and thus a liquid crystal panel having a high image quality can be accomplished. However, there is a problem that the manufacturing takt-time is lengthened by the applying work without lifting. Although using a plurality of syringes for shortening the manufacturing takt-time may be considered, the scale of equipment is enlarged and a lot of time is required in preparing the applying work.
In contrast, according to the seal printing method, which is the second method, a plurality of seal patterns can be spread at once, and thus the manufacturing takt-time can be greatly shortened. However, since the seal plate contact with the display area in the liquid crystal panel, an alignment layer may be damaged. The damage causes an alignment state of the liquid crystals to be scattered (abnormal alignment area) and to worsen the image quality. Further, in severe case, the damaged liquid crystal panel becomes defective product and cause to the yield deterioration.
The seal plate is configured to print the sealant on the glass substrate through interspaces of a mesh-shaped cloth, which is weaved a plurality of fibers in a lattice form, by pushing the sealant. To the areas where the sealant is not printed, a resin-shaped material, which is called an emulsion, is provided to distinguish the print areas.
Here, as shown in FIG. 6, due to the printing pressure and an sliding operation of a seal squeegee during the seal printing, cross-point sections of the mesh-shaped fiber are strongly pressed to the alignment layer of the glass substrate through the emulsion section. Thus, the alignment layer is damaged, and a large number of abnormal alignment areas (hereinafter referred to as “mesh marks”) 12 occur.
In one example of related arts, in order to suppress the occurrence of the mesh marks 12, a thickness of the seal plate around penetration sections is made to be thicker than a thickness of the display region, so that the seal plate do not contact with the alignment layer in the display area (see e.g. JP-A-H11-218773). Also, in one example of the related art, print protrusions are provided on the penetration sections of the sealant, so that the seal plate do not contact with the alignment layer in the display region (see e.g. JP-A-H06-64359).
However, even in either of the above-described cases, although an improvement to suppress the occurrence of the mesh marks 12 is accomplished, a uniform pressure is not applied over the entire seal plate during the seal printing process due to the change of the thickness of the seal plate. Thus, the width of the seal printed section becomes non-uniform (becoming thickened, cracked and the like). The non-uniformed printed section causes the finished quality of the seal print itself to deteriorate and also cause the yield in the seal printing process to deteriorate.
Accordingly, an object of the present invention is to suppress the yield deterioration in the seal printing process and to suppress the display-quality deterioration by the mesh marks 12 occurring during the seal printing.